Physics Project
The following is a project made by anonymous: INTRODUCTION
The general purpose photoconductive cell is also known as LDR – light dependent resistor. It is a type of semiconductor and its conductivity changes with proportional change in the intensity of light. There are two common types of materials used to manufacture the photoconductive cells. They are Cadmium Sulphide (CdS) and Cadmium Selenide (CdSe). Extrinsic devices have impurities added, which have a ground state energy closer to the conduction band since the electrons don't have as far to jump, lower energy photons (i.e. longer wavelengths and lower frequencies) are sufficient to trigger the device. Two of its earliest applications were as part of smoke and fire detection systems and camera light meters. The structure is covered with glass sheet to protect it from moisture and dust and allows only light to fall on it.
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Applications
Lead sulfide (PbS) and indium antimonide (InSb) LDRs are used for the mid infrared spectral region. GeCu photoconductors are among the best farinfrared detectors available, and are used for infrared astronomy and infrared spectroscopy. Analog Applications · Camera Exposure Control · Auto Slide Focus - dual cell · Photocopy Machines - density of toner · Colorimetric Test Equipment · Densitometer · Electronic Scales - dual cell · Automatic Gain Control – modulated light source · Automated Rear View Mirror Digital Applications · Automatic Headlight Dimmer · Night Light Control · Oil Burner Flame Out · Street Light Control · Position Sensor
*LDR has a disadvantage that when its temperature changes, its resistance changes drastically for a particular light intensity.
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AIM & APPARATUS
AIM: To study the variations, in current flowing in a circuit containing a LDR, because of a variation:(a) In the power of the incandescent lamp, used to ‘illuminate’ the LDR. (Keeping all the lamps at a fixed distance). (b) In the distance of a incandescent lamp, (of fixed power),
The general purpose photoconductive cell is also known as LDR – light dependent resistor. It is a type of semiconductor and its conductivity changes with proportional change in the intensity of light. There are two common types of materials used to manufacture the photoconductive cells. They are Cadmium Sulphide (CdS) and Cadmium Selenide (CdSe). Extrinsic devices have impurities added, which have a ground state energy closer to the conduction band since the electrons don't have as far to jump, lower energy photons (i.e. longer wavelengths and lower frequencies) are sufficient to trigger the device. Two of its earliest applications were as part of smoke and fire detection systems and camera light meters. The structure is covered with glass sheet to protect it from moisture and dust and allows only light to fall on it.
1
Applications
Lead sulfide (PbS) and indium antimonide (InSb) LDRs are used for the mid infrared spectral region. GeCu photoconductors are among the best farinfrared detectors available, and are used for infrared astronomy and infrared spectroscopy. Analog Applications · Camera Exposure Control · Auto Slide Focus - dual cell · Photocopy Machines - density of toner · Colorimetric Test Equipment · Densitometer · Electronic Scales - dual cell · Automatic Gain Control – modulated light source · Automated Rear View Mirror Digital Applications · Automatic Headlight Dimmer · Night Light Control · Oil Burner Flame Out · Street Light Control · Position Sensor
*LDR has a disadvantage that when its temperature changes, its resistance changes drastically for a particular light intensity.
2
AIM & APPARATUS
AIM: To study the variations, in current flowing in a circuit containing a LDR, because of a variation:(a) In the power of the incandescent lamp, used to ‘illuminate’ the LDR. (Keeping all the lamps at a fixed distance). (b) In the distance of a incandescent lamp, (of fixed power),